a) Field of the Invention
The present invention relates to a polyol, polyurethane resin, rigid polyurethane foam, preparation process thereof and a composite of said rigid polyurethane foam.
More particularly, the polyol of the present invention is a raw material for preparing a polyurethane resin having resistance to dissolving in hydrochlorofluorocarbons (hereinafter abbreviated as HCFC) and hydrofluorocarbons (hereinafter abbreviated as HFC) which as foaming agents cause very low public hazards. The polyol can provide a rigid polyurethane foam and a composite thereof, when used with the above foaming agents.
The rigid polyurethane foam has excellent properties which are equivalent to those of conventional polyurethane foams obtained by the use of chlorofluorocarbons (hereinafter abbreviated as CFC) as foaming agents. Hence, the rigid polyurethane foam of the present invention is extremely useful as an insulating material or insulating structural material for electric refrigerators, freezing ware houses, insulation panels, ships and vehicles.
b) Description of the Prior Art
In the conventional process of producing polyurethane foams, chlorofluorocarbons, particularly CFC-11 (trichlorofluoromethane) and CFC-12 (dichlorodifluoromethane) which are CFCs, have been used as a means of foaming. These materials have been recognized as hazardous and environmentally destructive materials as they decompose the ozone layer of the earth or enhance the green house effect. The production and use of these materials has recently been restricted. At the same time, attention has been directed to HCFC-123 (2,2-dichloro-1,1,1-trifluoroethane) and HCFC-141b (1,1-dichloro-1-fluoroethane), and additionally HFC-134a (1,1,1,2-tetrafluoroethane), HFC-152a (1,1-difluoroethane), as substitutes for CFC-11 and CFC-12. These substitutes, however, have a larger dissolving power with respect to polyurethane resins compared to CFC-11 and CFC-12, and thus are likely to significantly deteriorate polyurethane foam properties. For example, their use can decrease closed cell content and foam strengths. Heat insulation effects which are characteristic of rigid polyurethane foam can be significantly lowered because the above fluorocarbons dissolve walls of closed cells in the foam during the foaming reaction.
Consequently, a novel polyurethane resin has been desired. Conventional polyoxyalkylene polyols used as the raw material of polyurethane resins show a decrease in viscosity with an increase in the amount of added alkylene oxide. As a result, operations in polyurethane foam production can be conducted with ease. However, an excess addition of alkylene oxide leads to a dissolution of polyurethane resin in HCFC-123, HCFC-141b and HFC, and tends to make application of these foaming agents substantially impossible. On the other hand, when the amount of added alkylene oxide is reduced, the polyol becomes solid or extremely viscous and is very difficult to handle.
Japanese TOKKAI SHO 57-151613 (1982) and Japanese TOKKAI SHO 57-151614 (1982) disclose methods for blending low molecular weight polyols in order to decrease the viscosity of a mixture of an amine base polyol and an aromatic base polyester polyol (alkylene oxide was not added in the latter).
As mentioned above, in order to maintain resistance to dissolution in HCFC-123, HCFC-141b and HCF, operation efficiency in polyurethane foam production must be sacrificed significantly. A polyoxyalkylene polyol which has a viscosity suitable for the foaming operation and provides excellent mixing and dispersing capabilities in HCFC-123, HCFC-141b and HFC, has never been found.